Acoustic assessment of the austral sardine, Sprattus fuegensis, in the inner sea of the Chilean Patagonia

Abstract

The austral sardine (Sprattus fuegensis) is the target fish resource of a small-scale fishery operating in the Patagonian waters of Chile (41 • 30'S-46 • 00'S). Purse seine boats composed the fleet and landings have fluctuated between 14,344 and 48,589 tons during the period between 2006 and 2014. The stock assessment of the austral sardine utilizes a Statistical Catch-atLength model and this method requires independent estimates of abundance. In order to evaluate the abundance of the austral sardine in the inner sea of the Chilean Patagonia, an acoustic assessment was carried out in Autumn 2013. The study area covered the coastal zone of two administrative regions of Chile, the Los Lagos region in May 2013 and the Aysén region in June 2013. An EK-60 echo sounder permitted to obtain the acoustic data with transducer of 38 and 120 kHz from which echograms were examined to obtain NASC data. A total of 25 fishing set allowed to estimating the species composition and the length structure of the pelagic fish. In addition, fish confined in a jail allowed to estimating the target strength (TS) of the austral sardine. The fishing data and the NASC permitted to evaluate the acoustic biomass of the austral sardine, as well as the biomass of the anchovy (Engraulis ringens) and the common sardine (Strangomera bentincki). The biomass was estimated according to a stratified sampling design, the Gaussian Likelihood Geostatistics technique, and the fit to probability density models. The stratified design included six strata in the Los Lagos region and five strata in the Aysén region, as well as four depth strata (0-50, 50-100, 100-150 and 150-200 m). The stratified estimates of the austral sardine biomass were 118,173 tons (CV=11.6%) in the Los Lagos region and 101,630 tons (CV=9%) in the Aysén region. The estimates of biomass based on Gaussian geostatistics were 122,469 tons (CV=7.6%) in the Los Lagos region and 92,890 (70%) tons in the Aysén region. The best fitting of probability density functions to the acoustic density was log-normal, and allowed to estimate 100,145 tons of austral sardine in the Los Lagos region and 81,965 tons in the Aysén region. The biomass of anchovy was 50,079 tons in the Los Lagos region and 18,668 tons in the Aysén region. The biomass of common sardine was minimal with 5,327 tons in the Los Lagos region only. The estimate of the TS for the austral sardine was -67.59 dB and represented fish between 9 and 17 cm. The study area is spatially heterogeneous, and hydrographical features could determine behaviors of the austral sardine that have not yet described. Therefore, the estimates of biomass here obtained must be regarded as a relative abundance. The basis here obtained will be of importance for monitoring yearly changes in the abundance of the sardine austral.

First estimate of distribution, abundance, and risk of encounter with aquaculture vessels for the rare Chilean dolphin in the entire Northern Chilean Patagonia

“…Salinity information derived from oceanographic model output was particularly relevant for depicting high‐density areas for the species to the south of NCP, where there is greater freshwater input from glacier melting (González et al, 2011). Such coastal environments have been reported to hold several small pelagic fish species (Dyer, 2000; Cubillos et al, 2015) that might serve as prey for Chilean dolphins (Goodall & Galeazzi, 1985; Oporto & Brieva, 1990; Torres et al, 1992). Although many of these fish species have been associated with river mouths, either permanently or during some life‐history stages, none of them show such a restricted distribution as Chilean dolphins (Pequeño, 1989; Castro & Hernandez, 2000; Cubillos et al, 2007; Zunguza et al, 2022).…”

Sprattus fuegensis: Buratti, C., Díaz de Astarloa, J., Hüne, M., Irigoyen, A., Landaeta, M., Riestra, C., Vieira, J.P. & Di Dario, F.

“…Stock assessments are conducted by IFOP for the inland waters of the Los Lagos Region, but not for the Magellan Region (southern area). There is an artisanal fishery that targets this species in the Los Lagos and Aysen Region, which is in the northern part of its range in Chile (Cubillos et al 2015). It is not fished in the Magellan Strait region because the traditional fishery is located further north; however, as the population declines in the north, fishing effort has moved further south, and this is a concern.…”